Alkaline cyanide free zinc electroplating bath

ABSTRACT

1. AN ALKALINE, CYANIDE-FREE ZINC ELECTROPLATING BATH COMPRISING, IN AQUEOUS, CYANIDE-FREE ALKALINE SOLUTION A ZINC SALT IN AN AMOUNT SUFFICIENT TO PRODUCE ZINC DEPOSITS ON ELECTROPLATING, BETWEEN ABOUT 5 G./L. AND ABOUT 5 G./L. OF ROCHELLE SALT AS COMPLEXING AGENT, AND BETWEEN ABOUT 2 G./L. AND ABOUT 6 G./L. OF A PREFORMED CONDENSATION PRODUCT RESULTING FROM THE CONDENSATION REACTION OF EPICHLOROHYDRIN WITH THE SCHIFF BASE OBTAINED BY REACTING AN ALKYLENE POLYAMINE WITH AN OBTAINED BY REACTING AN ALKYLENE POLYAMINE WITH AN MOLAR RATIO OF SCHIFF BASE OF EPICHLOROHYDRIN BEING BETWEEN 1:0.5 AND 1:1.5.

US. Cl. 204-55 8 Claims ABSTRACT OF THE DISCLOSURE An alkaline cyanide-free zinc electroplating bath yielding brightzinc deposits comprises a zinc salt, a complexing agent and the reaction product of one or more alkylene polyamines, aldehydes and epichlorohydrin.

Preferably said reaction product is the condensation produ'ct'of an alkylene polyamine and an aromatic aldehyde of the general formula CHO wherein R is hydroxyl and/or lower alkoxy having from 1 to 4 carbon atoms and x is zero, one or two in a molar ratio from 1:05 to 1:1 which has been further reacted with epichlorohydrin in a molar ratio from 120.5 to 1:15. In addition, the bath may contain dimethylol thiourea.

BACKGROUND OF THE INVENTION It is known to use alkaline cyanide containing zinc electroplating baths in order to obtain bright zinc coatings on e.g. iron. As compared to acidic zinc baths and zinc baths free of cyanide, such cyanide containing zinc baths provide zinc deposits having good throwing power and metal distribution. Cyanide containing zinc baths generally contain about 10 to 150 g./l. of sodium cyanide which requires special waste disposal treatment and equipment to conform with legal provisions in connection with pollution control. These measures are very costly aud a burden to the economics of the process of zinc electroplating using cyanide baths.

Further alkaline cyanide-free zinc electroplating baths are known which do not require special pollution control measures. These known cyanide-free zinc baths, however, show far less favorable throwing power and metal distribution properties of the zinc coatings obtained therewith and further must be applied within a rather small range of current densities.

SUMMARY OI THE INVENTION It is an object of the invention to provide a cyanide-free zinc electroplating bath having the properties of an usual cyanide containing zinc bath thus yielding zinc coatings having good throwing power, metal distribution and very good brilliance. Further objects of the invention may be taken from the following description.

It has been found that bright zinc deposits having excellent throwing power and good metal distribution may be obtained from an alkaline cyanide-free zinc electroplating bath within a range of current densities of from 0.5 to 5.0 amps/dm. said bath comprising a zinc salt, sodium or potassium hydroxide, a complexing agent, such as potassium sodium tartrate (Rochelle salt) and, in addition, a reaction product of an alkylene polyamine, one or more aldehydes and epichlorohydrin. Preferably the bath should contain in addition dimethylol thiourea.

Urnited States Patent Patented Oct. 8, 1974 For preparing the reaction product of an alkylene polyamine, an aldehyde and epichlorohydrin as contained in the zinc bath of the invention in particular commercially available alkylene polyamines, such as diethylene triamine, triethylene tetramine and tetraethylene pentamine may be used. The alkylene polyamines are first reacted with one or more aldehydes in a molar ratio from 1:05 to 1:1 in aqueous solution at a temperature from 50 C. to 100 C., preferably from 70 C. to C. After cooling to about 40 C., the product obtained is reacted with epichlorohydrin at a temperature from 80 C. to C., such as 93 C. to 96 0., preferably in a molar ratio from 1:05 to 1:15.

As aldehydes in particular aromatic aldehydes of the formula -CHO wherein R is hydroxyl and/or lower alkoxy with 1 to 4 carbon atoms, in particular methoxy, and x is zero, one or two, may be used. Preferred aldehydes are salicyl aldehyde, anisaldehyde, vanillin, or veratraldehyde. Further unsaturated aromatic aldehydes, such as cinnamic aldehyde may be used.

When preparing the reaction product, preferred amounts are in the range of from 0.5 to 1 mole of aldehyde per mole of alkylene polyamine and 0.5 to 1.5 moles of epichlorohydrin per mole of the condensation product (Schiff base) of the alkylene polyamiue and the aldehyde(s).

The reaction product is preferably used in the electroplating bath of the invention in a concentration from 2' g./l. to 6 g./l. of the aqueous bath. Current densities from 0.5 to 5.0 amps/dm. may be used at a temperature from 15 C. to 35 C. The action of the reaction product in the electroplating bath of the invention may be considerably increased by adding dimethylol thiourea to the bath. The concentration of dimethylol thiourea preferably amounts to 0.05 g./l. to 1.0 g./l. of the bath.

Preferred zinc electroplating baths according to the present invention contain in aqueous solution 10 g./l. to 30 g./l. of zinc, calculated as zinc oxide and 100 g./l. to 250 g./l. of sodium hydroxide or potassium hydroxide and in addition thereto Rochelle salt or another complexing salt, dimethylol thiourea, and the reaction product of epichlorohydrin with the Schiif base obtained by condensing an alkylene polyamine such as diethylene triamine, triethylene tetramine, and/or tetraethylene pentamine with an aldehyde such as salicylaldehyde, anisaldehyde, vanillin, veratraldehyde, and/or cinnamic aldehyde in the molar proportions and amounts as given hereinabove.

The invention is further illustrated by the following examples.

EXAMPLE I An aqueous zinc electroplating bath is prepared from the following ingredients:

15 g./l. of zinc (calculated as zinc oxide), g./l. of sodium hydroxide, 2 to 5 g./l. of Rochelle salt, 0.05 g./1. to 1.0 g./l. of dimethylol thiourea, 2.0 g./l. to 5.0 g./l of the reaction product of triethylene triamine, anisaldehyde, and epichlorohydrin in a molar ratio of 1:0.5-121.

At a bath temperature from 15 C. to 35 C. using a current density from 0.5 to 5.0 amps/dm. brilliant zinc deposits on iron having excellent throwing power and metal distribution are obtained.

EXAMPLE II A zinc electroplating bath is prepared from the following ingredients:

30 g./l. of zinc (calculated as zinc oxide),

220 g./l. of sodium hydroxide,

2 g./l. to g./l. of Rochelle salt,

0.05 g./l. to 0.1 g./l. of dimethylol thiourea,

2 g./l. to 6.0 g./l. of a reaction product of tetraethylene pentamine, vanillin, and epichlorohydrin in a molar ratio of 1:0.51:1.

At a bath temperature of C. to 35 C. using a current density from 0.5 to 5.0 amps/dm. zinc deposits on iron having excellent brilliance, good throwing power and metal distribution are obtained.

EXAMPLE III A Zinc electroplating bath is prepared from the following ingredients:

At a bath temperature of from 15 C. to 35 C. using a. current density of from 0.5 to 5.0 amps/dm. zinc deposits on iron having excellent brilliance, good throwing power and metal distribution are obtained.

What is claimed is:

1. An alkaline, cyanide-free zinc electroplating bath comprising, in aqueous, cyanide-free alkaline solution a zinc salt in an amount sufiicient to produce zinc deposits on electroplating,

between about 2 g./l. and about 5 g./l. of Rochelle salt as complexing agent, and

between about 2 g./l. and about 6 g./l. of a preformed condensation product resulting from the condensation reaction of epichlorohydrin with the Schifi base obtained by reacting an alkylene polyamine with an aldehyde in the molar ration from 1:0.5 to 1:1, the molar ratio of Schitf base to epichlorohydrin being between 1:05 and 1:15.

2. The alkaline, cyanide-free zinc electroplating bath of Claim 6, additionally containing about 0.05 g./l. to 1.0 g./l. of dimethylol thiourea.

3. An alkaline, cyanide-free zinc electroplating bath comprising, in aqueous, cyanide-free alkaline solution.

a zinc salt in an amount sufficient to produce zinc deposits on electroplating,

between about 2 g./l. and about 5 g./l. of Rochelle salt as complexing agent, and

between about 2 g./l. and about 6 g./l. of the preformed condensation product resulting from reacting an alkylene polyamine with an aromatic aldehyde in the molar ratio from 1:05 to 1:1, the aromatic aldehyde being an aldehyde of the formula CHO in which R is a member selected from the group consisting of hydoxyl and lower alkoxy with 1 to 4 carbon atoms and x is one of the numerals zero, one, and two; and condensing the resulting Schiif base with epichlorohydrin in the molar ratio from 1:05 to 1:15.

.4 .4, I 4. The alkaline, cyanide-freezinc electroplating bath of Claim 11, additionally containing about 0.05 g ./l, to

' 1.4 g./l;'"of dimethylol thiourea.

5. An alkaline, cyanide-free zinc electroplating bath comprising, in aqueous solution,

between about 10 g./l. and about 30 g./l. of zinc, calculated as zinc oxide, between about g./l. and about: 250 g./l. of an alkali metal hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide, between about 2 g./l. and about 5- g./l. of Rochelle salt as complexingagent. I between about 0.05 g./l. and about thiourea, and between about 2 g./l. and about 6 g.'/l.'"of a preformed condensation productresultingfrom the condensation reaction of epichlorohydrin with 'theSchitf base obtained by reacting an alkylene polyamine with an aldehyde in the molar ratio from 110.5 to 1:1, the molar ratio of Schilf base to epichlorohydrin being between 1:05 and 111.5.

6. The alkaline, cyanide-free zinc electroplating bath of Claim 5, in which the preformed condensation product isa condensation product resulting from the reaction of about 1 mole of epichlorohydrin with the Schifi base obtained by reacting about 1 mole of an alkylene polyamine with about 0.5 moles to about 1 mole of an aldehyde. I

7. The alkaline, cyanide-free zinc electroplating bath of Claim 5, in which the preformed condensation product is a condensation product resulting from the reaction of about 1 mole of epichlorohydrin with the Schiff base obtained by reacting about 1 mole of an alkylene polyamine selected from the group consisting of diethylene triamine, triethylene tetramine, and tetraethylene pentamine and with about 0.5 moles to about l-mole of an aromatic aldehyde of the formula 1 g./l. of dimethylol CHO in which R is a member selected from the group consisting of hydroxyl and lower alkoxy with 1 to 4 carbon atoms and x is one of the numerals zero, one, and two. 8. The alkaline, cyanide-free zinc electroplating bath of Claim 5, in which the preformed condensation product is a condensation product resulting from the reaction of about 1 mole of epichlorohydrin with the Schifi base obtained by reacting about 1 mole of an alkylene polyamine selected from the group consisting of diethylene triamine, triethylene tetramine, and tetraethylene pentamine with about 0.5 moles to about 1 mole of an aromatic aldehyde selected from the group consisting of salicylaldehyde, anisaldehyde, vanillin, veratraldehyde', and cinnamic aldehyde.

References Cited UNITED STATES PATENTS 2,791,554 5/1957 Winters 20455 Y 2,451,426 10/ 1948 Bair et al. 204-55 Y 2,860,089 11/1958 Jackson 204-55 Y 3,227,638 1/1966 Burnson 20455,Y X 3,472,743 10/ 1969 Rushmere 204-55 Y 3,620,938 11/1971 Von Pless et al. 204 55;Y 3,655,534 4/1972 Kampe 20455 R 3,672,971 6/ 1972 Senge et al. 20455.R

GERALD L. KAPLAN, Primary Examiner" I us. 01. X.R.

204-Dig. 2 

1. AN ALKALINE, CYANIDE-FREE ZINC ELECTROPLATING BATH COMPRISING, IN AQUEOUS, CYANIDE-FREE ALKALINE SOLUTION A ZINC SALT IN AN AMOUNT SUFFICIENT TO PRODUCE ZINC DEPOSITS ON ELECTROPLATING, BETWEEN ABOUT 5 G./L. AND ABOUT 5 G./L. OF ROCHELLE SALT AS COMPLEXING AGENT, AND BETWEEN ABOUT 2 G./L. AND ABOUT 6 G./L. OF A PREFORMED CONDENSATION PRODUCT RESULTING FROM THE CONDENSATION REACTION OF EPICHLOROHYDRIN WITH THE SCHIFF BASE OBTAINED BY REACTING AN ALKYLENE POLYAMINE WITH AN OBTAINED BY REACTING AN ALKYLENE POLYAMINE WITH AN MOLAR RATIO OF SCHIFF BASE OF EPICHLOROHYDRIN BEING BETWEEN 1:0.5 AND 1:1.5. 